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Node.js - event emitter

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Created by:

Majid-Hajibaba

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In this article, we would like to show you event emitter in Node.js.

Introduction

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On the backend side, Node.js offers the option to build a system similar to JavaScript events in the browser such as mouse clicks, keyboard button presses, etc. This can be achieved using the Node.js events module.

Practical example

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The Node.js events module provides the EventEmitter class that is used to handle events.

1. Import EventEmitter using require():

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const EventEmitter = require('events');

2. Initialize EventEmitter object:

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const eventEmitter = new EventEmitter();

3. The object provides various methods. The most used are:

on - adds a callback function to be executed when the event is triggered,
emit - triggers an event.

Below we create a simple connect event that displays information about connection in the console.

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const EventEmitter = require('events');
​
// initialize object
const eventEmitter = new EventEmitter();
​
// create callback function
eventEmitter.on('connect', () => {
    console.log('connected');
});
​
// trigger the event
eventEmitter.emit('connect');